Field of the Invention
The present invention relates to a hot-water supply system comprising an instantaneous hot-water supply function.
Description of the Related Art
A hot-water supply system has conventionally been proposed which includes a hot water circulation circuit formed between a hot-water supplier and a mixing faucet to achieve an instantaneous hot-water supply function (for example, see Japanese Patent Laid-Open No. 8-121800 (hereinafter referred to as Patent Document 1)). In this hot-water supply system, the hot water circulation circuit is constituted by providing a bypass passage that bypasses the mixing faucet by making a water outlet passage and a hot-water outlet passage communicate with each other, the water outlet passage being branched from a water supply passage that supplies water to the hot-water supplier and being connected to a water side connection port of the mixing faucet, the hot-water outlet passage being configured to feed hot water from the hot-water supplier.
According to the configuration of the hot water supply system disclosed in Patent Document 1, it is not necessary to provide an exclusive return passage that connects a hot-water side connection port of the mixing faucet to the water supply passage of the hot-water supplier. Accordingly, construction can easily be conducted and cost of the hot-water supply system can be reduced.
In the hot-water supply system disclosed in Patent Document 1, the bypass passage bypassing the mixing faucet is equipped with a check valve configured to block water flow from the water outlet passage side to the hot-water outlet passage side, and a temperature responsive valve configured to be closed when hot-water temperature inside the bypass passage is equal to or more than a prescribed temperature.
The hot-water supply system disclosed in Patent Document 1 executes circulation heating operation to heat hot water inside the circulation circuit, which is constituted of the water supply passage, the water outlet passage, the hot-water supplier, the hot-water outlet passage, and the bypass passage, by operating a circulating pump to circulate hot water through the circulation circuit, while operating a burner in the hot-water supplier to heat a heat exchanger communicating with the water supply passage and the hot-water outlet passage.
When high-temperature hot water is fed from the hot-water supplier while the circulation heating operation is performed, the temperature responsive valve is closed and circulation of hot water in the circulation circuit is stopped, so that the high-temperature hot water is prevented from flowing to the water outlet passage side through the bypass passage. This prevents discharge of the high-temperature hot water which has flown to the water outlet passage-side, when a user opens the mixing faucet.
In the hot-water supply system disclosed in Patent Document 1, the temperature responsive valve provided in the bypass passage is closed when high-temperature hot water is fed to the hot-water outlet passage from the hot-water supplier while the circulation heating operation is performed. However, it takes a certain time for the temperature responsive valve to shift from an opened state to a closed state.
It is therefore difficult to perfectly prevent the high-temperature hot water from flowing into the water outlet passage-side during a period until the temperature responsive valve is closed after the high-temperature hot water starts to flow into the bypass passage from the hot-water outlet passage.
To overcome this difficulty, it can be considered to limit the flow rate of the hot water circulating through the circulation circuit during circulation heating operation to decrease the amount of the high-temperature hot water flowing into the water outlet passage side at the time when the temperature responsive valve is being closed. However, when the flow rate of the hot water circulating through the circulation circuit becomes less than a specified flow rate which is an operating condition of the burner, the burner fails to operate and therefore the circulation heating operation cannot be carried out.